The invention relates to a crystalline form of a bisphosphite ligand.
Bisphosphites are commonly used as ligands for transition-metal catalyzed reactions such as hydroformylation and hydrocyanation. One commonly used bisphosphite ligand is 6,6′-[[3,3′,5,5′-tetrakis(1,1-dimethylethyl)-[1,1′-biphenyl]-2,2′-diyl]bis(oxy)]bisdibenzo[d,f][1,3,2]-dioxaphosphepin, (hereinafter Ligand A), shown in Formula 1:

Like many organic molecules, Ligand A is a crystalline material capable of existing in a number of forms. A crystalline non-solvate and various solvate forms are disclosed in U.S. Pat. No. 8,796,481 and Yuan Hao, et al. “Crystal Structure of 6,6′-(3,3′5,5′-tetra-tertbutylbiphenyl-2,2′-diyl)Bis(oxy)didibenzo[d,f]-[1,3,2]dioxaphosphepine” Chinese J. Struct. Chem., Vol 31, 673 (2012).
US 2014/0288322 A1 discloses a process for preparing a fast drying form of Ligand A via treatment with a secondary alcohol, e.g., isopropanol, at 72-75° C. for several hours. The crystal structure of the resulting material is not disclosed. U.S. Pat. No. 8,796,481 describes the means to make the non-solvate form of Ligand A as well as a number of solvates. Preparation of the crystalline non-solvate thus described also requires elevated temperatures, e.g., at least 65° C. and preferably above 85° C. While both the form of Ligand A described in US 2014/0288322 A1 and U.S. Pat. No. 8,796,481 are suitable for hydroformylation applications, elevated temperatures are required to produce them. Exposing bisphosphites to elevated temperatures may increase decomposition and thereby lower the yield of the valuable product.
Alternatively, one may choose to produce a crystalline solvate; however, adding the solvate form of a ligand into an industrial hydroformylation process would, by definition, introduce the accompanying solvent of crystallization as a contaminant. In addition, the amount of said solvent of crystallization is variable depending on the drying conditions and does not contribute to the hydroformylation reaction, i.e., the solvent acts as a diluent or filler in the solid ligand.
A third alternative would be to prepare and use a desolvated form, but effectively drying solvated materials is known to take days under forcing conditions; see US 2014/0288322 A1. Such procedures can also result in decomposition, e.g., oxidation due to extended handling, and will increase the production time and, therefore, the cost of manufacture.
Thus, it would be desirable to have a form of Ligand A that dries quickly, is thermally stable, and that can be prepared via a facile, cost-effective process that avoids prolonged exposure to elevated temperatures. Heretofore, the Ligand A crystal structure of the invention, hereinafter designated Ligand A′, has not been recognized.